1. Field of the Invention
The present invention relates to a system and method for controlling a multi-cylinder internal combustion engine having electronically controlled airflow to provide a similar output torque characteristic under varying atmospheric conditions.
2. Background Art
Various engine control strategies have been developed to compensate for changes in available engine power or torque due to ambient conditions, such as temperature and barometric pressure. When driving a vehicle at high altitude, for example, conventional mechanical throttle control systems would seem sluggish or underpowered compared to sea level or lower altitudes across the entire range of accelerator pedal positions. This also created challenges in calibrating shift points for automatic transmissions, which were often based on accelerator pedal position, because the same pedal position resulted in a different output torque depending upon the ambient operating conditions.
An object of the present invention is to provide a system and method for controlling an engine which produces a smooth and continuous increase in wheel torque relative to accelerator pedal position at any altitude and ambient temperature while delivering the same torque for a given pedal position at all altitudes and ambient temperatures where sufficient torque is available.
In carrying out the above object and other objects, features, and advantages of the present invention, a system and method for controlling a multi-cylinder internal combustion engine include determining a currently available maximum torque, determining a driver demanded torque based on a current accelerator pedal position and reference ambient conditions, and controlling the engine to deliver the lesser of the driver demanded torque and a calibratable percentage of the currently available maximum torque.
The present invention provides a number of advantages. For example, the present invention provides a similar torque at high altitudes as at sea level for a given low pedal position while smoothly blending into the currently available peak torque. The greater torque available at high altitude for lower pedal positions is preferred by some drivers. In addition, the present invention provides a model based approach which requires less calibration effort and is more robust to intended consequences which may otherwise result from an approach requiring more complex calibrations.
The above advantages and other advantages, objects, and features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings.